This invention relates to articles molded from flake-like wood particles and, more particularly, to such articles having non-planar portions, such as material handling pallets and the like.
Considerable effort has been devoted to developing techniques for molding articles including non-planar portions from inexpensive residue and surplus woods. One area of particular interest for utilizing such woods is in the production of material handling pallets having at least the same strength and durability and other desirable characteristics of standard pallets constructed from lumber.
It is well known to manufacture flat or substantially flat structural boards or so-called particle board from comminuted wood by mixing the wood particles with a suitable resinous binder, such as a synthetic thermosetting resin, forming the mixture into a multilayered mat and then compressing the mat between heated platens to set the binder and bond the wood particles together. This type process is exemplified in U.S. Pat. Nos. 3,164,511, 3,391,233 and 3,940,230.
Molding of pallets and other articles including non-planar portions presents problems of little or no concern in the manufacture of flat or substantially flat particle board. For instance, one difficulty involved in molding pallets is the necessity to pull or draw a plurality of hollow legs having acceptable crushing strengths from a substantially flat mat of wood particles without adversely affecting the strength of the deck member or the legs. Consequently, the above type process for manufacturing particle board heretofore has not been employed to manufacture pallets or other similar articles from wood particles.
In one prior art method for molding pallets from wood particles, exemplified by U.S. Pat. Nos. 3,104,085, 3,359,929 and 3,611,952, wood fibers are made into a pulp slurry which typically also contains a resinous or other suitable binder. The slurry is introduced into a mold wherein most of the water is removed by compressing, application of a vacuum or positive pressure, etc. The wet, molded pallet is transferred to a heated mold and dried under elevated pressure and temperature conditions to expedite removal of water, and to cure the binder if one is included in the slurry. If a binder is not included in the slurry, the dried pallet usually is dipped into a resin containing solution for strengthening and water proofing. This prior art method involves several expensive processing steps and the pallets produced thereby do not have acceptable strength characteristics or durability for many applications.
In another prior art for molding pallets from wood particles, promoted in the United States under the trademark "WERZALIT" and exemplified by U.S. Pat. Nos. 3,146,285 and 3,354,248, a mixture of finely comminuted wood particles and a heat curable, resinous binder is introduced into a cold press to form a preform having nearly the final size and shape of the pallet, with partial or no curing of the binder. The preform is transferred to a heated press or mold wherein it is compressed to the final size and shape at an elevated temperature to completely cure the binder. This method is relatively expensive because of the degree to which the starting material must be comminuted, the amount of binder required to bond the relatively small wood particles together, the capital investment for the different presses, and the operating costs associated with the numerous processing steps.